1. Field of the Invention
This invention relates to an address translation control system, and, more specifically to an address translation control system in a data processing system providing the function of performing a storage protection check by storing a storage protection key in an address translation buffer such as a Translation Lookaside Buffer (TLB), which executes control in such a way that if the storage protection check is not required, a translated pair of a translation result is not registered in the address translation buffer when the desired translation pair does not exist in the address translation buffer and a dynamic address translation system is utilized.
2. Description of the Related Art
In an existing data processing system employing a multi-virtual storage system, a dynamic address translation system for translating an effective address into a physical address is included. Moreover, also provided is an address translation buffer TLB which stores results, once translated, in the form of a translation pair and the contents of the buffer is utilized for further address translation. The TLB is always used for each execution of a memory access instruction. It is used not only when an effective address is a logical address and it is necessary to translate a logical address into a physical address but also when an effective address is a real address, because the TLB is also utilized for translating a real address into a physical address. The TLB also employs a structure for storing a storage protection key, for protecting storage, which is previously stored on said address translation buffer and a storage protection check is carried out simultaneously with the address translation utilizing the fact that the address translation buffer is indexed or accessed at the same time as a memory access. Namely, even when an effective address is a real address, a translation pair is stored in the address translation buffer together with the storage protection key and the address translation buffer is indexed at the time of memory access by a real address and a check of the storage protection key is carried out. Here, a real address is different from a physical address. A physical address is uniquely assigned to locations within the main storage unit (MSU) hardware. A real address is a virtual physical address for each computer when plural computers or plural virtual computers use the MSU in common. However, some memory access instructions, called privileged instructions, are not required to perform a memory protection check. In the case of above type instruction, an effective address generally means a real address. In such a case, when an address translation buffer hit does not occur, entry of a translation result into the address translation buffer may be an inefficient update of the buffer because the contents of the address translation buffer is replaced by an effective address which does not require a storage protection check. Privileged instructions can change a storage protection key and a storage protection check is not necessary during the execution of such an instruction. Such an instruction is useful in changing the scope of protection. An IBM 370 is a system that includes a storage protection key which requires privileged instructions to change the key.